The Adaptations of the Galapagos Penguin For a Harsh and Unpredictable Environment


Albert Chan

Darwin, Evolution and the Galapagos

William Durham

October 7, 2002


 

 

I. Introduction

Due to its previous isolation from the contact of man, the Galapagos Penguin (Spheniscus mendiculus) is one of the least studied penguin populations in the world. The only species of penguin that is found above the equator, the Galapagos Penguin is now being studied extensively, and it is observed that the Galapagos Penguin possesses many unique features that help it survive in the Galapagos Islands. Due to the extreme temperatures and unpredictable ocean currents, the Galapagos Penguin has been forced to adapt morphologically and physiologically in ways that other species of penguins never have had to. In addition, the Galapagos Penguin even demonstrates specialized behaviors that help it cope with the extreme heat and unpredictable food supply found in the Galapagos.



II. Life of the Galapagos Penguin

The Galapagos Penguin lives only in the Galapagos Islands, and is believed to have descended from the Humboldt Penguins (Wildland Adventures, 2002). Humboldt Penguins presently live in colonies all along the western coast of South America, and it is likely that the Galapagos Penguin originated from a stray group of Humboldt Penguins that followed the cold waters of the Humboldt Current to the Galapagos Islands. The Galapagos Penguin is similar in appearance to the Humboldt Penguin with the major exceptions of a longer, more slender bill, fewer white feathers, and smaller overall size (Stonehouse, 2002).

Galapagos Penguin

Despite having very few natural predators (hawks, snakes, and rats may eat the eggs or baby chicks), the Galapagos Penguin is still an endangered species. Because of the Galapagos Penguin's dependence on a sporadic food source produced by the Cromwell Current, it is estimated that there are as few as two or five thousand Galapagos Penguins left on the islands of Fernandina and Isabela Islands (Jackson, 2002). Lying between the South Equatorial Current and the islands of Fernandina and Isabela, the Cromwell Current's waters are sometimes pushed up toward their shores (Peterson, 1979). These upwellings result in enormous concentrations of little fish, which compose the penguins' entire diet (Boersma, 1978). However, due to the unpredictability of ocean currents, which are even further complicated by temperature fluctuations caused by El Niño (Boersma 1998), the food supply varies tremendously, and the continued survival of the Galapagos Penguin is often threatened.

In addition to the sporadic supplies of food, the Galapagos Penguin must cope with extreme temperatures of hot and cold. The Galapagos Penguin hunts in 59-82 degrees Fahrenheit waters while living on islands shores that can get as hot as 104 degrees Fahrenheit (Peterson, 1979). Forced to hunt for fish in cold ocean waters, and to live out the rest of their time in the hot Galapagos sun, the Galapagos Penguin demonstrates morphological, physiological, and possibly even behavioral adaptations.


II. Morphological Adaptations

At 53 cm long, the Galapagos Penguin is the third smallest penguin species in the world. Because the Galapagos Penguin lives in the hottest environment of all penguins, natural selection most likely shaped the Galapagos Penguin's smaller body size. Because it is much more effective to dissipate heat in a smaller body, natural selection would have favored a smaller and more compact body structure. The Humboldt Penguin, the ancestral species of the Galapagos Penguin, is 65 cm long, almost 25 percent longer than the Galapagos Penguin. Because of the dramatic size differences between the Galapagos Penguin and its ancestral species, natural selection (and not genetic drift or other random factors) certainly shaped the evolution of the smaller size of the Galapagos Penguin. The less productive Galapagos shores probably also contributed to the smaller sizes of the Galapagos Penguin. It is very likely that a smaller body size of the Galapagos penguin is a consequence of the reduced supply of food available to the Galapagos Penguin (when compared to other penguin species). The size of Antarctic penguins, for instance, supports the hypothesis that cold weather and dependable food supplies selects for bigger penguin size. In contrast to the Galapagos Penguins, Antarctic penguins live in a frigid environment with a rich and dependable seasonal food supply (Know, 1970; Raymont, 1963), and can consequently grow up to three or four feet, more than twice the size of the Galapagos Penguin.

Because of the warmer weather, the Galapagos Penguin has achieved other general, morphological adaptations. In contrast to the Antarctic penguins, the Galapagos Penguin and other tropic penguins have fewer, looser feathers as well as bare areas around the eyes and at the base of the bill in which to lose heat (Reilly, 1994). This sharp contrast between the Artic birds and those of tropic birds further supports the idea that the looseness of feathers and the presence of bare skin are important adaptations to warmer weather. Relative to other penguins, the Galapagos Penguin also has thinner layers of fat, which is also an advantage when living in warm weather and possessing limited food resources.

 

III. Physiological Adaptations

To cope with oscillating supplies of food, the Galapagos Penguin has adapted many physiological features. Arctic penguins have an annual, stable breeding cycle that corresponds to an annual plankton boom. In stark contrast, the Galapagos Penguin shows a much wider variation in their breeding cycle, most likely due to the unpredictable upwelling of the Cromwell Current (Boersma, 1976). Figure 1 demonstrates the Galapagos Penguin's huge variability in breeding activity. Many other birds demonstrate similar behavior in that they have variable breeding cycles in environments with fluctuating resources. For instance, Swallow-tailed Gulls, which rely on the same fish that the Galapagos Penguins eat, have a breeding season that varies considerably (Snow and Snow, 1967). Similarly, in locations around the world, the Northern Blue Penguin, the Black-footed Penguin, and the Humboldt Penguin all depend on unstable currents or food supplies, and subsequently, all show great variability in their breeding cycles (Davis, 1955; Kinsky, 1930).


Figure 1. The black lines represent breeding activity of the Galapagos Penguin. This figure demonstrates the wide variety of breeding times for the penguins.

The most unique adaptation of the Galapagos Penguin, however, is its molting. Unlike every other species of penguins that molts only once a year, the Galapagos Penguin molts twice in a year. More frequent molting protects the Galapagos Penguin by frequently replacing the Galapagos Penguin's insulating layer of feathers that may easily be damaged by the strong equatorial sun (Peterson, 1979). Boersma has noted the necessity for frequent molting because of her observations that the sun bleaches penguin features brown and algae often grows on the breast, belly, and flippers. (Boersma, 1975) In addition, whereas most other penguin species molt after breeding, the Galapagos Penguin molts before its nesting season. Molting after the breeding season for the Galapagos Penguin is an adaptation that is reflective of the unpredictable and limited food supply of the Galapagos Penguins. When living with abundant food resources, other penguins molt and fast after their chicks are fledged because it allows the new fledglings to learn how to hunt with less competition from the adult penguins (Carrick and Ingham, 1967). In contrast, it is more advantageous for the Galapagos Penguin to molt before breeding because it may not be assured of sufficient food to complete its molt if it molts after breeding (Reilly, 1994). In addition, a sharp, unexpected drop in available food during a pre-breeding molt would allow the Galapagos Penguin to postpone breeding until more favorable conditions arise. Pre-breeding molting sometimes results in Galapagos Penguins that cannot breed because it molts too late into the breeding season. The postponement of breeding, at first glance, is an evolutionary disadvantage because it limits immediate progeny, but it is believed that one's exclusion from breeding is still favorable for the survival of one's genes because it increases one's chances of survival for the next breeding season (Boersma, 1976).

In addition to being the only penguin that molts twice a year, the Galapagos Penguin is the only penguin species that demonstrates an adaptation called hatching asynchrony. Whereas other penguins lay two eggs that usually hatch within 24 hours within one another (Warham, 1973), the Galapagos Penguin hatches its two eggs between two to four days apart (by laying and incubating its eggs at slightly different times). When food supplies grow and decline at random intervals (which the Cromwell Current is often responsible for), hatching asynchrony provides a better chance that at least one of the chicks will survive (Boersma, 1976).

IV. Advantageous Behaviors

In addition to its numerous adaptations that were shaped by natural selection, the Galapagos Penguin also exhibits many important behavioral characteristics that allow it to survive in the unpredictable and harsh environments of the Galapagos Islands. To keep from overheating, for instance, the Galapagos Penguin exhibits several obvious behaviors that include panting, seeking shade on land, hunting in the ocean during the day (and staying on land at night), and opening their wings 45 degrees to the cooling breeze (Reilly, 1994). The Galapagos Penguin also exhibits less obvious behaviors that counteract the extreme temperatures of the Galapagos. For instance, relative to most other penguins, the Galapagos Penguin is less social in nest laying and hunting. To keep their eggs from overheating, Galapagos Penguins often make solitary nests among shade-providing lava beds (Jackson, 2000). Also, because group hunting is more effective in waters that have a lot of fishes (Boersma, 1978), the Galapagos Penguins are found hunting in pairs much more often that other species of penguins. The Galapagos Penguins do hunt in groups (especially during "feeding frenzies" that consist of large groups of birds hunting together for hours), but when El Niño warms the waters (Boersma, 1998) or upwelling of the Cromwell Current fails to occur, the Galapagos Penguins are much more likely to hunting solitarily or in pairs.

V. Conclusion and Future of the Galapagos Penguin

The Galapagos Penguin is a remarkable species that exhibits numerous unique adaptations that allow it to continue surviving in one of the most extreme niches of all penguins. Still, the Galapagos Penguin is an endangered species whose fate is precariously dependent on constantly changing ocean currents. If the Cromwell Current fails indefinitely or moves away from the Galapagos Islands, or El Niño permanently changes the temperatures of the Galapagos coasts, the Galapagos Penguin may go extinct soon afterwards. In addition, feral animals introduced by man are also taking its toll. Animals such as wild dogs and cats, have been observed eating eggs, chicks, and even adult penguins, and should be contained immediately. So far, no human intervention has been made to preserve and provide support for the Galapagos Penguins, but more research needs to be done to decide how humans should preserve the unique species of the Galapagos Penguin.


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